The invention relates to a method for operating a drive device with an internal combustion engine and with an exhaust gas system connected to the internal combustion system, which exhaust gas system has at least one catalytic converter to which a hot air stream which is heated by means of a heating device is supplied for heating. The invention also relates to a drive device
The drive device serves for example for driving a motor vehicle. The drive device can be a part of a hybrid drive device, which beside the drive device has at least one further drive device, which for example has an electric machine in particular only the electric machine. Hereby it can be provided that the drive device and the further drive device, at least temporarily in cooperation, generate a torque for driving the motor vehicle. For this purpose the drive device and the further drive device are for example operatively connected with each other by means of a transmission. Beside the internal combustion engine, the drive device includes the exhaust gas system. The exhaust gas system serves for discharging the exhaust gas generated by the internal combustion engine in the direction of the external environment of the drive device. In order to meet exhaust gas provisions it is required to at least partially purify the exhaust gas before it reaches the external environment. For this purpose the exhaust gas system has the catalytic converter. When passing through the exhaust gas system the exhaust gas of the internal combustion engine is conducted through the catalytic converter in which a catalytically favorable reaction, in particular a reduction, takes place. After passing through the catalytic converter the exhaust gas can be conducted into the external environment by the exhaust gas system.
The catalytic converter usually has to have a defined operating temperature, in order for the reaction to take place and for the purification of the exhaust gas to be performed. The catalytic converter is heated on one hand by way of the exhaust gas which flows through the catalytic converter and which downstream of the internal combustion engine has a high temperature. In particular at low external temperatures and/or a cold start of the drive device, however, the time period that passes until the catalytic converter reaches the operating temperature, may be relatively long. In this time period the reaction cannot occur or can only occur at low efficiency so that the exhaust gas is not reliably or not completely purified.
This problem is particularly pronounced in the hybrid drive device because in this case the internal combustion engine is not constantly in operation. This means that in time periods in which only the further drive device is operated for providing a torque, while the drive device and with this the internal combustion engine is deactivated, the catalytic converter is not heated by the exhaust gas. Correspondingly its temperature decreases. When the temperature falls below the operating temperature, the exhaust gas generated when reactivating the drive device or the internal combustion engine cannot reliably be purified.
For this reason the heating device is provided by means of which the hot air stream is generated and subsequently supplied to the catalytic converter in the at least one operating state of the internal combustion engine for heating the catalytic converter. As a result of operating the heating device, the catalytic converter can thus be maintained at or above its operating temperature also during time periods in which the internal combustion engine is not operated or in which it is deactivated. The heating device is in particular provided in internal combustion engines that are constructed as diesel internal combustion engines. According to the above, the catalytic converter can be heated directly by means of the heating device. This means that the heating device is not or at least not only connected with the catalytic converter in heat transfer connection via a thermally conducting connection. Rather, a fluid for generating the hot air stream is heated and subsequently the catalytic converter is heated by means of the hot air stream.
The temperature that can be achieved by means of the heating device is usually very high and—at least immediately downstream of the heating device—is above the maximally permissible temperature of the catalytic converter. For this reason it can be provided that the heating device for generating the hot air steam is only operated during operation of the internal combustion engine and to mix the hot air stream into the exhaust gas of the internal combustion engine upstream of the catalytic converter. The exhaust gas usually has a temperature that is lower than the temperature of the hot air stream. In the case of a sufficient exhaust gas stream the temperature of the fluid, which flows through the catalytic converter and is composed of the hot air stream and the exhaust gas of the internal combustion engine, is thus sufficiently low and preferably corresponds to at least the operating temperature, however, it is lower than the maximally permissible temperature of the catalytic converter.
However, when the exhaust gas stream is too low, for example because the internal combustion engine is deactivated, the temperature of the hot air stream at optimal efficiency of the heating device is too high. Therefore it can be provided to decrease the efficiency of the heating device to lower the temperature to a degree that is appropriate for the catalytic converter. Such a lowering of the efficiency, however, means that the potential of the heating device is not fully realized and in addition the amount of generated pollutants is greater compared to an operation with optimal efficiency.
From the state of the art for example the printed publications DE 43 20 880 A1 and DE 44 10 820 A1 are known. The former relates to a control device for introducing air into an exhaust gas line of an internal combustion engine. Hereby it is provided to operate a heating device when a start switch is activated. In addition air is to be introduced into an air intake line during and after the start of the internal combustion engine, however, a control valve is not to be open during a predetermined time period T1 after switching on the star switch. The latter printed publication discloses an additional air supply device for an internal combustion engine and a gas heating device for the air supply device.
It is therefore an object of the invention to provide a method for operating a drive device that does not have the aforementioned disadvantages, but enables in particular in each operating state of the internal combustion engine a reliable heating of the catalytic converter by means of the heating device, while at the same time ensuring a low pollutant emission.
According to the invention this is achieved with a method for operating a drive device, including heating a hot air stream with a heating device integrated in a cylinder head of an internal combustion engine of the drive device, said internal combustion engine being connected with an exhaust gas system; mixing the hot air stream upstream of a catalytic converter with a cold fresh air stream for adjusting a defined temperature of the hot air stream; and supplying the hot air stream having the adjusted defined temperature to the catalytic converter in at least one operating state of the internal combustion engine so as to heat the catalytic converter. Hereby it is provided that the hot air stream is mixed upstream of the catalytic converter with a cold fresh air stream for adjusting a defined temperature. It is thus not or not only provided to adjust the temperature of the fluid supplied to the catalytic converter by means of the exhaust gas of the internal combustion engine. Rather the hot air stream is to be combined with the cold air stream prior to flowing through the catalytic converter. In addition it can be provided, in particular when the internal combustion engine is activated, that also the exhaust gas of the internal combustion engine is combined upstream of the catalytic converter with the hot air stream.
The cold fresh air stream consists of fresh air, which is withdrawn from an external environment of the drive device. The fresh air is in particular chemically unaltered, i.e., it has not participated in a chemical reaction, for example combustion or the like, in the drive device. The fresh air of the cold fresh air stream has a temperature that is lower than the temperature of the hot air stream. By selecting an appropriate mass flow of cold fresh air, the defined temperature can be adjusted upstream of the catalytic converter. The defined temperature hereby corresponds for example to the operating temperature of the catalytic converter, above which the catalytic converter enables a complete catalytic reaction. The temperature can, however, also be higher or lower, however it is below the maximally admissible temperature of the catalytic converter. The cold fresh air stream is conducted past the heating device, i.e., it does not flow through the heating device.
By mixing the hot air stream with the cold fresh air stream, the mass flow of the fluid flowing through the catalytic converter is increased. At the same time the temperature is adjusted to a degree that is appropriate of the catalytic converter. Due to the increase of the mass flow, the catalytic converter is heated faster and more evenly than would be possible by means of the hot air stream alone. In addition as explained above, the heating device can be operated with optimal efficiency and/or with lower pollutant emission.
A further embodiment of the invention provides that the cold fresh air stream is conducted through at least one deactivated cylinder of the internal combustion engine or a cylinder of the internal combustion engine that is operated in the trailing throttle mode. The cold fresh air stream thus flows through the cylinder of the internal combustion engine prior to being mixed with the hot air stream and is subsequently supplied to the catalytic converter. For this purpose the valves of the cylinder, in particular at least one inlet valve and at least one outlet valve, are correspondingly adjusted. For example the at least one inlet valve and the at least one outlet are simultaneously opened so that the cold fresh air stream can flow unimpeded through the cylinder.
The cylinder can hereby be deactivated or can be operated in a trailing throttle mode. In both cases no combustion of fuel takes place in the cylinder, so that the cold fresh air stream is not chemically altered when flowing through the cylinder. When the cylinder is deactivated, preferably the entire internal combustion engine is deactivated. When the internal combustion engine is activated, i.e., when it is supplied with fuel or when combustion of fuel takes place in the internal combustion engine, this is not the case for at least one cylinder through which the cold fresh air stream is conducted. For this purpose the cylinder is for example operated in the trailing throttle mode, i.e., the piston assigned to the cylinder is merely moved by at least one further, activated cylinder and/or by an externally provided torque.
A further embodiment of the invention provides that a cold air stream conducted to the heating device is branched off from the cold fresh air stream at a withdrawal point upstream of the internal combustion engine. Up until the withdrawal point the cold air stream and the cold fresh air stream are conducted together, for example in a common line. Together, the cold airstream and the cold fresh air stream form a fresh air stream, which is withdrawn from the external environment of the drive device. At the withdrawal point, the fresh air stream is divided into the cold air stream and the cold fresh air stream. The cold air stream is supplied to the heating device and heated by the heating device so that the cold air stream becomes the hot air stream. The cold fresh air stream on the other hand is, as explained above, conducted so as to circumvent the heating device and, downstream of the heating device, however upstream of the catalytic converter, is united again with the hot air stream, which originated from the cold air stream. The cold fresh air stream hereby for example passes through the at least one cylinder of the internal combustion engine.
A refinement of the invention provides that a fresh air stream which forms the cold air stream and the cold fresh air stream is compressed upstream of the withdrawal point by means of a compressor. As mentioned above, upstream of the withdrawal point the cold air stream and the cold fresh air stream are conducted together in the form of the fresh air stream and are only separated at the withdrawal point. In addition it is provided that this fresh air stream is compressed by means of the compressor. The fresh air stream thus is to be brought to a higher pressure level and subsequently divided into the cold air stream and the cold fresh air stream at the withdrawal point. The compressor is for example an electrically operated compressor or a supercharger, in particular a blower, for example an electrically operated or supported blower.
In a particularly advantageous embodiment of the invention, it is provided that at least one inlet valve and at least one outlet valve of the cylinder are operated so that the cold fresh air steam is conducted in the direction of the catalytic converter. Particularly preferably this is the case when the cylinder, through which the cold fresh air stream is conducted, is operated in the trailing throttle mode. In this case the piston of the cylinder is periodically displaced by at least one further cylinder of the internal combustion engine and/or the externally provided torque. By correspondingly adjusting the inlet valve and the outlet valve, a pumping effect can thus be achieved. By means of this pumping effect the mass flow of the cold fresh air stream can be increased and/or adjusted in a targeted manner. In order to achieve a most continuous pumping effect, it is of course advantageous when the cold fresh air stream is conducted in parallel through multiple cylinders that are operated in the trailing throttle mode.
A refinement of the invention provides to use a burner, which is operated with liquid or gaseous fuel as heating device. Such a burner is particularly suited for the here provided indirect heating of the catalytic converter. The burner is preferably operated with liquid and/or gaseous fuel. The fuel is for example introduced into a mixture-generating chamber of the burner through a fuel conduction line. An air supply line can also lead into the mixture-generating chamber. Correspondingly air and also fuel can be conducted into the mixture-generating chamber and subsequently combusted for heating the catalytic converter. In this way the catalytic converter can be brought very quickly to the desired operating temperature so that a purification of the exhaust gas can be performed with high efficiency. The advantage of the burner is a very high energy density, a variable mounting position and a simple construction. Particularly preferably the heating device is constructed according to the heating device described in patent application DE 10 2012 016 673. The mentioned patent application is incorporated herewith by reference for a preferred embodiment of the invention. In particular the drive device can additionally have the features of one or more of the claims of the mentioned patent application in addition or alternatively to the already present features.
It can further be provided that an electrically operated or electrically supported compressor is used as compressor. The compressor can also be exclusively operated electrically or electrically supported. In the latter case it is for example part of a charger, which can be constructed as compressor or as exhaust gas turbo charger.
It can also be provided that the compressor is part of an exhaust gas turbo charger, as mentioned above. Particularly preferably, the exhaust gas turbo charger is electrically supported, so that the compressor can be used for compressing the fresh air stream also when the internal combustion engine is deactivated, by operating the compressor purely electrically. The exhaust gas turbo charger can, however, also be electrically supported in case the exhaust gas mass stream, which is generated by the internal combustion engine and supplied to the exhaust gas turbo charger, is not sufficient to sufficiently compress the fresh air stream.
The invention also relates to a drive device, in particular for implementing the method described above, with an internal combustion engine and with an exhaust gas system, which is connected to the internal combustion engine, and which has at least one catalytic converter to which a hot air stream heated by a heating device can be conducted in at least one operating state of the internal combustion engine for heating the catalytic converter. It is provided that the exhaust gas device is configured to mix the hot air stream upstream of the catalytic converter with a cold fresh air stream to adjust a defined temperature. The advantages of such an approach or such a construction of the drive device have already been discussed. The drive device and the method implemented therewith can be refined according to the above description so that reference is made to thereto.
In an advantageous embodiment of the invention it is provided that the heating device is integrated in a cylinder head of the internal combustion engine. In such an arrangement a particularly compact or space-saving arrangement of the heating device is possible. This is in particular the case when the mixture-generating chamber of the heating device is formed directly in the cylinder head of the internal combustion engine, for example by casting. In this context reference is again made to the patent application 10 2012 016 673 whose features can be advantageously used for refining the invention in addition to the features described herein.